1. Field of the Invention
The present invention relates to a surface light source apparatus used in a transmissive type or semi-transmissive type display device.
2. Background Art
In a conventional surface light source apparatus, a rubber holder is attached to a bent corner portion of a U-shaped fluorescent discharge tube and a light guide plate is attached adjacent to the rubber holder, as disclosed in JP-A-2000-194280.
In a liquid crystal display device disclosed in JP-A-2003-29262, a light guide plate is fixed by a protrusion formed on a metallic chassis, and an L-shaped fluorescent discharge tube is inserted between a rising portion of the metallic chassis and a fixed post included in a resin cabinet to hold the light guide plate and the L-shaped fluorescent discharge tube.
In an edge-light type backlight disclosed in JP-A-2001-35235, a light guide plate is positioned by a pawl formed by cutting and erecting a portion of a casing formed by processing metal such as aluminum, and the light guide plate and a U-shaped fluorescent discharge tube are received in the casing.
In the conventional lighting unit disclosed in JP-A-2000-194280, since the rubber holder is provided in the bent corner portion of the U-shaped fluorescent discharge tube, the tube wall temperature of the bent corner portion of the U-shaped fluorescent discharge tube is reduced to be lower than that of a portion, in which the rubber holder is not provided, by at least 5° C., due to heat transmission to a back cover and a casing.
In the liquid crystal display device disclosed in JP-A-2003-29262, since the L-shaped fluorescent discharge tube is inserted between the fixed post and the metallic chassis, the tube wall temperature of the fluorescent discharge tube is reduced due to heat transmission to the metallic chassis.
In the edge-light type backlight disclosed in JP-A-2001-35235, since the U-shaped fluorescent discharge tube is received in the casing formed of aluminum, the tube wall temperature of the fluorescent discharge tube is reduced due to the heat transmission to the casing.
Particularly, in a cold cathode fluorescent lamp (hereinafter, referred to as CCFL) which is a narrow tube having an outer diameter φ of about 2.4 mm (inner diameter: 1.8 mm), which is being employed so as to realize slimness, compactness and high brightness, mercury in the CCFL is condensed (unevenly distributed) at a bent corner portion of the U-shaped CCFL having a low temperature due to the characteristics thereof. Accordingly, the amount of mercury necessary for a light emitting portion lacks in the CCFL, and thus the lifetime of the CCFL is reduced to a short time such as several hundreds to several thousands hours (halving of initial brightness) even in a general use state. The tube wall temperature of a portion other than the bent corner portion is reduced and thus the brightness deteriorates due to the condensation (uneven distribution) of mercury.